The invention relates to a method of orienting the angular position of a workpiece with an optically detectable structure relative to a reference direction.
The method is particularly but not exclusively applicable to the manufacture in the semi-conductor industry of transistors, wherein a plurality of semiconductive elements are deposited successively on a substrate. In such a process, it is often necessary to deposit such semi-conductive elements with a high degree of accuracy and for this purpose masks are frequently employed which shield predetermined portions of the substrate from the means depositing the semi-conductive elements. The method is particularly applicable to the task of accurately and rapidly locating such masks relative to the substrate.
It is known in the semi-conductor industry to adjust masks for the illumination thereby, that one aligns sights on their discrete structures with the aid of split field microscopes and then carries out an orientation by hand or automatically. With regard to an automatic orientation with reference to angular position (rotation) and local position (coordinates x and y), it is advantageous initially to undertake the orientation of the angular position and only then the correction of the locality, since then no coupling with the rotation is any longer present, which would require a multi-loop control system. It is an object of the present invention to provide a method and an apparatus for automatically accomplishing the orientation of the angular position.